The intent of the proposed research is to extend our present knowledge of the mechanism of action of RNA polymerase. The specific aims of the project are: 1. Studies on the effect of synthetic templates containing pyrimidine analogues on enzyme binding, chain initiation and elongation. 2. The role of RNA polymerase in nucleotide selection with special regard to the uniqueness of the initiation nucleotide site. 3. The role of tryptophan in RNA polymerase structure and function. 4. Reconstitution of RNA polymerase containing chemically modified a sigma or alpha subunits in order to define the role of these subunits.